1. Field of the Invention
This invention relates to an electric heating apparatus, more particularly to an electric heating apparatus capable of converting electric energy from various batteries having different voltages into thermal energy.
2. Description of the Related Art
FIGS. 1 and 2 show a conventional electric heating apparatus that includes a control box 940 and a heating wire 913 electrically connected to the control box 940.
The heating wire 913 is bent to form several segments for uniformly heating an area. The heating wire 913 may be replaced by a different type of electric heating component in the form of a tube or a block.
The control box 940 is adapted to receive a battery set 930, and includes a switch 921 and a temperature control unit 922. The switch 921 is user-operable for starting up the conventional electric heating apparatus. The temperature control unit 922 is capable of detecting temperature of the heating wire 913, and providing an electric current from the battery set 930 to the heating wire 913 according to the detected temperature. When the switch 921 is switched on, the electric current is provided from the battery set 930 and flows through the heating wire 913 such that the heating wire 313 can convert electric energy into thermal energy.
However, the conventional electric heating apparatus may not accept batteries of various sizes and having different voltages. In other words, the conventional electric heating apparatus may only use a particular sized battery having a particular voltage.
A thermoelectric apparatus disclosed in U.S. Pat. No. 5,576,512 is compatible with multiple power sources each providing a different voltage. The thermoelectric apparatus includes a sensing circuitry, a parallel connection circuitry, a serial connection circuitry, and thermoelectric devices. The sensing circuitry is capable of detecting whether the power source provides a lower operating voltage or a higher operating voltage. For the lower operating voltage, the thermoelectric devices are electrically connected to one another in parallel through the parallel connection circuitry. For the higher operating voltage, the thermoelectric devices are configured in series through the serial connection circuitry. As a result, the thermoelectric apparatus is switchable between a full heating mode, where the thermoelectric devices are in the parallel connection, and a half heating mode where the thermoelectric devices are in the series connection.
However, circuits of the thermoelectric apparatus as described above are complicated. Furthermore, the thermoelectric apparatus may not generate a constant output power when the power sources have different operating voltages.